Stability of rapid-processed photographic materials



United States Patent 3,212,895 STABILITY OF RAPID-PROCESSED PHOTOGRAPHICMATERIALS Jean Barbier, Paris, and Jean-Pierre Fauchille, Vincennes,

France, assignors to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey No Drawing. Filed Dec. 20, 1960, Ser. No.77,009

5 Claims. (Cl. 96-61) This invention relates to photography and moreparrticularly to an iriiprovement in stabilization of rapidly processedphotographic materials.

Rapid processing of photographic materials is known. Stabilization ofsuch rapidly developed silver images is known using solutions ofcompounds such as alkali metal and ammonium thiocyanates andthios-ulfates, or alkali metal and ammonium compounds of thiourea andthioglycolic acid. In rapid processing it is customary to eliminate thefixing and washing steps and to stabilize the developed image bytreatment with a solution of a compound which does not react withmetallic silver and which forms a light-stable silver complex byreaction with undeveloped silver halide. While the methods known in theart are satisfactory for the stabilization of silver images which arenot to be stored under adverse conditions, there is the disadvantagethat such silver images tend to fade when stored under conditions ofhigh temperature and humidity. Consequently, rapid processing has hadlittle appeal for use in preparing prints that are to be stored for anylength of time, for example, in office files.

It is, therefore, an object of the present invention to providerapid-processing emulsions capable of being stabilized to produce printshaving improved stability to high temperature and humidity. A furtherobject is to provide a rapid-processing method for silver halideemulsi-on layers which produces prints having improved stability tostorage at high temperature and humidity.

These objects are accomplished by the method described herein whichincludes treating a rapidly processed silver halide emulsion layer witha solution of an alkali or ammonium bisulfite and formaldehyde. Theselect mixture of our invention can advantageously be incorporated inthe silver halide emulsion directly or it can be used as a separatetreating bath after conventional stabilization with a stabilizingcompound such as ammonium thiocyanate. In either event, the selectmixture is effective in preventing fading on storage of rapidlyprocessed prints in a humid environment. Particularly subject to fadinghas been thiocyanate-stabilized silver images which have been known tobecome almost illegible after a few months storage in a humidenvironment. We have now found that rapid processed prints can bepreserved using the novel combination of our invention such that copiescan be obtained which have a stability nearly equal to a photographtreated by standard sodium thiosulfate and wash means. The improvedprint stability obtained using particular combinations of this inventionwas not obtained where either of the components of the combination wasemployed alone.

The stabilizing process customarily used in the preparation of rapidlyprocessed prints which are further stabilized according to our inventionis described in Brice US. Patent 2,448,857, issued September 7, 1948,and in Broughton et al. US. Patent 2,614,927, issued October 21, 1952.According to the process, a silver halide photographic emulsion,preferably a gelatin-silver halide emulsion, is exposed in the usual wayand developed with a suitable silver halide developing solution. Afterdevelop- 3,212,895 Patented Oct. 19, 1965 ment, the excess developingsolution present on the surface of the print is removed by anyconvenient means such as squeegee, and the print is then treated with astabilizing solution. The purpose of the stabilizing agent is to makethe undeveloped silver halide substantially incapable of change onfurther light exposure. The stabilizing agent must be a compound whichdoes not react with metallic silver and which forms a light-stable,silver complex by reaction with the undeveloped silver halide in theemulsion layer. Stabilizing agents described for this purpose in Yackelapplication Serial No. 594,589 and in Broughton et al. US. Patent2,614,927, issued October 21, 1952, are compounds containingdoublebonded sulfur or an SH linkage, such as alkali metal and ammoniumthiosulfates and thiocyanates, thiourea and thioglycolic acid.Additional stabilizing agents which may be employed in the stabilizingof layers preserved according to our invention are described in RussellUS. Patent 2,453,346, issued November 9, 1948. In the use of suchstabilizing agents the resulting silver complex should be light coloredor transparent so that there is no interference with the viewing orprinting of the final image.

According to our invention any of the above-described stabilizing agentscan be employed. However, alkali metal and ammonium thiocyanatestabilizing agents are preferred. In the practice of our invention wemay use a thiocyanate stabilizing compound, such as ammoniumthiocyanate, and in addition, we further stabilize so as to give anincreased preservation of the silver image using a combination of abisulfite and formaldehyde. The bisulfite compounds of our invention canbe alkali metal or ammonium bisulfites, e.g., sodium metabisulfite,potassium metabisulfite, ammonium metabisulfite, or ammonium, potassium,or sodium bisulfite. The formaldehyde is conveniently used as an aqueoussolution. The concentration of the water-soluble alkali bisulfitecompounds can vary as an ingredient in the aqueous solution of theformaldehyde-bisulfite mixture from as little as 1.0 percent to as highas 15 percent of the total weight of the aqueous solution. Thepercentage of formaldehyde in the formalin-bisulfite solution can varyfrom as little as 1.5 percent to as high as about 8 percent of the totalvolume. When the select mixture is added to the emulsion, suitableproportions of a solution containing from about 5 to about 10 percent ofbisulfite and 4 to 6 percent formaldehyde can be used. This solutionwhen added to the emulsion is added in an amount from about 8 percent toabout 12 percent of the total emulsion volume. Alter natively, thebisulfite, e.g., sodium bisulfite or potassium metabisulfite can beadded in solution directly to the emulsion separately from theformaldehyde solution if the latter is added to the emulsion in excessof the amount needed for emulsion-hardening purposes. Preferably,however, the bisulfite is first dissolved in the aqueous formaldehydesolution prior to addition to the emulsion, e.g., wherethiocyanate-stabilized images are to be treated by bathing in thebisulfite-formaldehyde mixture, the bisulfite is present in an amount offrom about 5 percent to about 10 percent of the weight of a 4 percentformaldehyde aqueous solution. These concentrations are based on atreatment or immersion time in the bath of about 30 seconds. Lowerconcentrations can be used with longer application or immersion times.The time will vary with the nature of the film, that is, the grain size,chemical composition, and with the temperature of treat ment. Formalinwhich is an aqueous solution containing about 37 percent formaldehyde byweight is a convenient source of the formaldehyde.

The process of our invention is particularly adaptable to improving thekeeping characteristics of developed silver images which have beenstabilized with solutions of thiocyanate although the treatment alsoimproves the image stability where other stabilizing compounds, such assodium thiosulfate have been used. It was found that the smaller thegrain size of the emulsion-s, the more critical and diificult it becameto insure satisfactory stability. It is deduced from this fact that theimage deterioration is a surface phenomenon.

The emulsions used in this invention can advantageously be hardenedemulsions. The emulsions may be hardened with any suitable hardener forgelatin such as formaldehyde, a halogen-substituted aliphatic acid suchas mucobromic acid as described in White U.S. Patent 2,080,019, or bycompounds such as those described in US. Patents 2,725,294, 2,725,295,and 2,725,305. The emulsions may be coated on paper or other opaquesupports or on any of the well known transparent supports such ascellulose nitrate, cellulose acetate, polyethylene terephthalate,polystyrene, polycarbonates, etc.

The developing agents which are incorporated into the emulsions,rapidly-processed and stabilized according to our invention, can bedeveloping agents such as 3,4-dihydroxydiphenyl, 2,3 -dihydroxydiphenyl,and hydroquinone compounds (e.g., hydroquinone, chlorohydroquinone,methylhydroquinone, etc.), 3-pyrazolidones (e.g.,1-phenyl-3-pyrazolidone, 4-methyl-l-phenyl-3-pyrazolidone,4,4-dimethyl-1-phenyl-3-pyrazolidone, etc). These developing agents canbe incorporate-d into the emulsion substantially as indicated in theexamples herein described.

My invention will be further illustrated by reference to the followingspecific examples:

Example 1 The following example illustrates a manner of improving thestability of rapidly-processed photographic prints according to ourinvention.

An emulsion suitable for use in our invention was made as follows:

Solutions were made of (a) 25 grams of gelatin in 1 liter of water at 40C., (b) 100 grams of silver nitrate .in 500 cc. of water at 20 C., and(c) 35 grams of sodium chloride in 500 cc. of water. Solutions (b) and(c) were simultaneously run into solution (a) at a uniform rate whilestirring the latter over a period of about 10 minutes. Solution (b) wasnot allowed to run in faster than (c). Thereafter, 150 grams of gelatinin 1200 cc. of water at 40 C. were added. 25 grams of3,4-dihydroxydiphenyl were then dissolved in 250 cc. of methyl alcohol.This solution was slowly added to the above mixture. The emulsion washardened by using a suitable gelatin hardening agent such asformaldehyde. Following the hardening of the emulsion, 300 grams of a 4percent formaldehyde solution containing percent by weight of sodiummetabisulfite was added with stirring. The emulsion was then coated on apaper support over an area of about 500 square feet. Samples of thedried product were then exposed in a number of ways to a subject,including by contact with or projection of a negative and by reflexexposure with a subject comprising printed matter on a paper base.Thereafter the exposed samples of the element containing a developingagent in the emulsion were treated for about 60 seconds in an aqueousalkaline solution of the following composition:

Grams Sodium carbonate monohydrate 50 Sodium hydroxide 5 Sodiumthiosulfate (crystalline) 2 Potassium bromide 12 Water to make 1 liter.

The above alkaline developing solution was applied with a sponge. Afterdevelopment, the surface was squeegeed and the unfixed element was thentreated for about 60 seconds with the following solution of astabilizing agent applied with a sponge:

Ammonium thiocyanate grarns 320 Sodium fluoride grams 4 Chrome alum (2%solution) ml Acetic acid (99.5%) ml 40 Sodium metabisulfite grams 50Water to make 1 liter.

The developing and stabilizing treatments can also be accomplished byother means, e.g., by rolling the exposed element down onto a padmoistened with the processing solution. After processing, the samplesmade and processed as outlined in this example were compared to controlstrips that were identically made and processed, except that no additionof metabisulfite and formaldehyde was made to the emulsion. The stripswere hung in a wet oven at F. and 98 percent relative humidity. Thesilver images on the test strips containing the sodium metabisulfite andformalin were still clearly legible after nine days, whereas in thecontrol strips the image faded in about seven hours.

Example 2 The following example illustrates the improvement in silverimage stability obtained by treatment of thiocyanate-stabilizedrapidly-processed images in a treating solution containing sodiummetabisulfite and formalin.

An emulsion suitable for use in our invention was made as follows:

Solutions were made of (a) 25 grams of gelatin in 1 liter of water at 40C., (b) 100 grams silver nitrate in 500cc. of water at 20 C., and (c) 35grams of sodium chloride in 500 cc. of water. Solutions (b) and (0) weresimultaneously run into solution (a) at a uniform rate while stirringthe latter over a period of about 10 minutes; solution (b) preferablynot being allowed to run in faster than (c). Thereafter, grams ofgelatin in 1500 cc. of water at 40 C. were added. To this solution,then, was added 250 cc. of methyl alcohol containing 25 grams of3,4-dihydroxy-diphenyl. The emulsion was then hardened with formaldehydeand coated on paper support over an area of about 500 square feet. Theproduct was then exposed, developed, and stabilized as described inExample 1.

After stabilization, various strips of the material were treated using avariety of reducing agents including hydroquinone, ascorbic acid,formalin, and a solution of sodium 'metabisulfite and formaldehyde. Thefollowing table shows the various results obtained where these compoundswere used in a treating solution following stabilization in ammoniumthiocyanate. The treated paper strips and untreated controls were storedat 120 F. and a relative humidity of 98 percent. Treatment of the paperstrips was accomplished by rolling the stabilized element down onto a.pad which was moistened with the preserving compound in solution. Thefollowing test results were obtained:

Treatment alter stabilization control Stability at 120 F.,

No after treatment Image lasted 2 hours. 5% Hydroquinone solution Imagelasted 4 hours.

5% Sodium metabisulfite s01ution Image lasted 7 hours.

5% Ascorbic acid solution Image lasted 5 days.

4% Formaldehyde solution Image lasted 3 days.

4% Formaldehyde and 5% sodium metabi- Image lasted more than sulfite. 8days.

ly-processed silver images is obtained where the additive of ourinvention is employed.

It is apparent that some reaction occurs between the bisulfite andformaldehyde when aqueous solutions thereof are mixed to produce analkali metal (or ammonium) formaldehyde bisulfite (sometimes called asulfoxylate), and that this product can be added to the emulsion, ortreating bath, instead of the mixtures mentioned above. It is importantthat a source of bisulfite ion and formaldehyde be available in thestabilization treatment, and the source thereof is not important. Ofcourse, when a metabisulfite is dissolved in water, this provides thebisulfite ion (HSO A metabisulfite is essentially an anhydride of abisulfite, e.g., Na S O is the anhydride of NaHSO As mentioned, ouremulsions are preferably gelatinsilver halide emulsions. However, We arenot limited thereto since other water-permeable organic colloid vehiclesmay be used for dispersing the silver salt and developing agent, e.g.,polyvinyl alcohol, partially hydrolyzed polyvinyl esters and celluloseesters, etc.

It is apparent from the foregoing description of our invention that asubstantial proportion of the silver compounds remains in the emulsionafter the stabilizing treatment. This differs from the customary fixingand washing in which the intent is to remove the residual silver halidefrom the emulsion.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the scope and spirit of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. In a rapid process for the formation of a silver image in a silverhalide photographic layer which comprises:

(a) exposingsaid layer,

(b) developing a silver image in said layer with a silver halidedeveloping agent, and

(c) stabilizing said silver image and silver halide by treating saidlayer with a solution of a compound selected from the class consistingof the alkali metal thiocyanates, the alkali metal thiosulfates,ammonium thiocyanate, ammonium thiosulfate, thiourea and thioglycolicacid, until substantially all the residual silver halide is converted toa light stable silver complex, the improvement comprising the step of(1) contacting the stabilized silver image and silver complex in saidlayer with an aqueous solution of formaldehyde and a compound selectedfrom the class consisting of an alkali metal bisulfite, ammoniumbisulfite, an alkali metal metabisulfite and ammonium metabisulfite topreserve the said stabilized image and silver complex in said layeragainst fading produced by storage at elevated temperatures and elevatedhumidity.

2, The process of claim 1 in which the preserving step comprises thecontacting of a rapidly developed and stabilized photographic silverhalide element with an aqueous solution of formaldehyde and sodiumbisulfite.

3. A light-sensitive photographic element for rapid processingcomprising a support having coated thereon a silver halide emulsioncontaining:

(a) a silver halide developing agent, and

(b) a silver image preservative comprising aqueous formaldehyde and amember selected from the class consisting of an alkali metal bisulfite,an alkali metabisulfite, ammonium bisulfite and ammonium metabisulfite.

4. A light-sensitive photographic element for rapid processingcomprising a support having coated thereon a silver halide emulsioncontaining:

(a) a silver halide developing agent selected from the class consistingof 3,4-dihydroxydiphenyl, 2,3-dihydroxydiphenyl, a hydroquinone and a3-pyrazolidone, and

(b) a silver image preservative comprising aqueous formaldehyde andsodium formaldehyde bisulfite ad dition complex.

5. A light-sensitive photographic element for rapid processingcomprising a support having coated thereon a silver halide emulsioncontaining:

(a) a silver halide developing agent selected from the class consistingof 3,4-dihydroxydiphenyl, 2,3-dihydroxydiphenyl, a hydroquinone and a3-pyrazolidone, and

(b) a silver image preservative comprising aqueous formaldehyde andammonium formaldehyde bisulfite addition complex.

References Cited by the Examiner UNITED STATES PATENTS 710,568 10/02Eichengrun 9661 1,941,852 1/34 Brunken 96111 1,954,512 4/34 Allison 96612,571,725 10/51 Kimball et a1. 96-85 2,614,927 10/52 Broughton et al.9661 2,845,349 7/58 Schwarz 9666 2,865,745 12/58 Chan et al. 96282,902,367 9/59 Welliver et al. .a 9666 3,030,209 4/62 Henn et a1. 9666 X3,079,858 3/63 Haydn et al 9635 3,080,230 3/63 Haydn et al. 9695 OTHERREFERENCES Noller, Chemistry of Organic Compounds, pp. 199- 200,Saunders and Co., Philadelphia (1951).

Yule, Journal of the Franklin Institute, vol. 239, pp. 221-230, 1945.

NORMAN G. TORCHIN, Primary Examiner.

HAROLD N. BURSTEIN, ABRAHAM H. WINKEL- STEIN, Examiners.

1. IN A RAPID PROCESS FOR THE FORMATION OF A SILVER IMAGE IN A SILVERHALIDE PHOTOGRAPHIC LAYER WHICH COMPRISES: (A) EXPOSING SAID LAYER, (B)DEVELOPING A SILVER IMAGE IN SAID LAYER WITH A SILVER HALIDE DEVELOPING,AND (C) STABILIZING SAID SILVER IMAGE AND SILVER HALIDE BY TREATING SAIDLAYER WITH A SOLUTION OF A COMPOUND SELECTED FROM THE CLASS CONSISTINGOF THE ALKALIL METAL THIOCYANATES, THE ALKALI METALL THIOSULFATES,AMMONIUM THIOCYANATE, AMMONIUM THIOSULFLATE, THIOUREA AND THIOGLYCOLICACID, UNTIL SUBSTANATIALLY ALL THE RESIDUAL SILVER HALIDE IS CONVERTEDTO A LIGHT STABLE SILVER COMPLEX, THE IMPROVEMENT COMPRISING THE STEP OF(1) CONTACTING THE STABILIZED SILVER IMAGE AND SILVER COMPLEX IN SAIDLAYER WITH ANA AQUEOUS SOLUTION OF FORMALDEHYDE AND A COMPOUND SELECTEDFROM THE CLASS CONSISTING OF AN ALKALI METAL BISULFITE, AMMONIUMBISULFITE, AN ALKALI METAL METABIISULFITE AND AMAMONIUM METABISULFITE TOPRESERVE THE SAID STABILIZED IMAGE AND SILVER COMPLEX IN SAID LAYERAGAINST FADING PRODUCED BY STORAGE AT ELEVATED TEMPERATURE AND ELEVATEDHUMIDITY.